# Principles of Thermodynamics [closed]

A gas expands and does 82.7 J of work on the surroundings. At the same time, the gas loses 103 J of energy to the surroundings as heat. What is the change in the internal energy of the gas? would this be ΔE = q + w (-103) + (82.7) = -20.3. I get confused with the positive and negative charges.

• Ignore the heat part first. If the gas does work on its surroundings, do you think its energy increases or decreases? If you push a block of metal, does your energy increase or decrease? Commented Oct 16, 2015 at 21:37
• This seems like a homework question. We ‎have a policy which states that you should show your thoughts and/or efforts into solving the ‎problem. It'll make us certain that we aren't doing your homework for you. Otherwise, this ‎question may get closed.
– bon
Commented Oct 17, 2015 at 10:23
• – user7951
Commented Nov 12, 2015 at 16:17

The standardized definition of the change in internal energy $U$ for a closed thermodynamic system is
$$\Delta U = Q + W$$
where $Q$ is amount of heat transferred to the system and $W$ is work done on the system (provided that no chemical reactions occur).